The present invention relates to silicone compositions for rendering surfaces non-adherent, more particularly to a solvent-free releasing agent silicone composition.
Conventionally, the most common agents for rendering surfaces non-adherent are manufactured in the form of a compound diluted in some organic solvent, which is generally called a solvent-type releasing agent. However, the trouble with such releasing agents is that the use of an organic solvent, which needs to be evaporated after application, results in lowering of the energy efficiency as well as in environmental pollution, and they are always dangerous for workers. In order to solve this problem, so-called solvent-free releasing agents have been developed which use virtually no solvent (examples of these are found in Japanese Patent Publication No.52-47485 and Japanese Patent Publication No.52-39791). Another solution to the same problem is a silicone-containing releasing agent in the form of an aqueous emulsion (for example, the one described in Japanese Patent Publication No.57-53143).
An example of a known solvent-free releasing agent silicone composition is a curable agent which has two main ingredients, namely a diorganovinylpolysiloxane having both ends stopped with a vinyldimethylsilyl group [CH.sub.2 .dbd.CH--Si(CH.sub.3).sub.2 --], and an organohydrogenpolysiloxane having at least two hydrogen atoms directly bonded to silicon atoms, which ingredients undergo an addition reaction (as described in Japanese Patent Publication No.52-39791; Japanese Laid open Patent Application No.57-77395; Japanese Laid-open Patent Application No.50-141591).
However, it has been experienced and reported that the cured film obtained from the above-described solvent-free releasing agent silicone composition tends to be more brittle, lower in slip factor, and excessively lower in the minimum force required for peeling, especially under a high-speed peeling condition, than that obtained from conventional solvent-type releasing agent silicone compositions. Although various modifications have been made so as to improve the above-mentioned three properties of the cured film of the solvent-free releasing agent, no known solvent-free releasing agent is endowed with all of these three qualities. For example, a solvent-free releasing agent silicone composition described in Japanese Laid-open Patent Application No.61-159480 has an improved slip factor, but is still unsatisfactory with respect to the film toughness and the minimum force required for peeling in the case of high-speed peeling.
To improve these properties, it has been proposed to increase the degree of polymerization of the diorganovinylpolysiloxanes themselves which are contained in the solvent-free releasing agent or to admix the diorganovinylpolysiloxanes with organopolysiloxanes having a high degree of polymerization. The results so far of such proposals have been such that although improvements are noticeable in the three properties, the curability of the silicone composition is lowered, the uniformity in the minimum requisite peel force is sacrificed, and the residual adhesive strength of the adhesive is weakened.